| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | difficult [to-vb] at [adj] [noun sg] | 17 |
|
| 2 | difficult [to-vb] at [det] [noun sg] | 12 |
|
| 3 | difficult [to-vb] at this [noun sg] | 8 |
|
| 4 | difficult [to-vb] at this [noun sg] | 8 |
|
| 5 | difficult [to-vb] at [adj] stage | 5 |
|
